Need some help with front pipe exhaust leak. I had to take front pipe off to do oil pan and gasket repair.

Ever since I put it in on, I get exhaust leaks coming from under the hood of the car. At first I thought it was temporary I didn't see it at first. But then I realized when you drive the car or rev it up. The exhaust comes from below. The first I time I checked it, I put my hand (waited until car cooled down of course!) all around the flange connection to feel for gaps, I didn't feel any gaps. Then I tried to take the exhaust header manifold heat shield cover off. I didn't take it completely off. But just enough to move it around. And I looked and I didn't see any holes. I didn't notice any.

I think my next step is to do it again, this time rev the engine and then see where the leak is coming from with the exhaust header manifold heat shield off.

I used a metal ring gasket for that front pipe when I had a mechanic install the front pipe (a while back). I thought with metal gaskets you don't have to reinstall them do you? Or maybe I didn't torque the bolts to spec. Even though it's flat on there. Maybe if I tightened them up a little more? Maybe it's just one bolt, I noticed one bolt went in there rough. It went in there like it was tightening to the left. And feeling loose going in right. Then I just took it out and put it back in again (And torqued it snug it correctly) (Or maybe I didn't). Anybody have any ideas on what I should do?

 

Definitely locate the leak first. You may be able to use some soapy water to look for bubbles from an exhaust leak.

Once the source is located, then you can inspect gaskets, bolts, the mating surfaces for issues.

 

Year & version of your car?

What's that "metal ring gasket"?
Some years have a solid-metal ring that fits between flanges (with springs on the bolts) to allow for some flex & misalignment. Some have a hollow metal ring that installs in a groove just like an O-ring. The O-ring type should be replaced, because they frequently leak if reused.

Another trick to find the leak... Have someone hold a wad of rags against the tailpipe when the engine is running. Just enough pressure to cause the leak to make more noise so it's easier to find.

 

Honda 1993 accord LX automatic transmission. Front pipe is a Bosal 840-493 VFM 2114. And I believe the ring gasket is part number Bosal 256-1125..

If the metal ring can be replaced. I assume that it doesn't weld or melt in there? It's a ring that is shaped like an O. But I'm not sure what you mean by hollow? I don't think it's a hollow metal ring.

 

I've had other cars with similar ring gaskets, and those ring gaskets are made from hollow tubing. I could tell that by the weight, but you could also tell by crushing it with a pliers (after you have a new one in your hands).

There's a groove machined into one flange, the other flange is flat. When the ring fits into the groove, it sits above the surface and crushes a bit to make the seal. Sometimes they're coated with some kind of softer metal that helps it seal. When you take the flange apart, it doesn't spring back up so that means it doesn't always seal if you reuse it. These are typically used at the connection between the exhaust manifold & the A-pipe.

The solid type is much more fat, like a donut. With those, the flanges are made so they don't come together completely; there's like 1/4" space between the 2 flanges, and the bolts have springs on them. Typically used between the A-pipe and the catalytic converter to allow for some flexing.

 

Yeah, I just had it rechecked out by a mechanic. Yep, I was suppose to install a new one. He told me that I had to get out old one with a pic and put a new one in.
It doesn't seem to be that bad anymore when I rev it up. The mechanic saw nothing. It seems like a come and go problem. I said I was worried that the exhaust leak could get into the cabin of the car. He told me it wasn't that bad and that would take days of running the car.

Maybe it's resealing itself after running the car more. I'm hoping

 

A ghetto way to fix it is to get some muffler paste - it's kinda like cement that hardens with heat. Smear it on the flanges then bolt em together. But that messes up your chances of doing it "right" with a new metal O-ring.

If you're in the habit of idling when parked, then getting exhaust into the car can be a concern. When you're actually driving there's a lot of air blowing through the engine compartment. The other thing is exhaust blowing onto the outside of the oxygen sensor, messing up the measurement.

 

Yeah, I think I'm going to have him do it, maybe. If it acts up again and I smell it during idle again. The rings cost $10.00 each I believe. Oh well. I did so much work not to do it myself. He is very fair on the pricing. It was just more of, I wanted to feel satisfied I have done the job myself type thing. Thanks for mentioning the idle thing, even I was a little worried about that.

I do believe if that I just start the car right up and not drive it and it idles. I don't see or smell the exhaust fumes. And now when I drove it to his shop. I forget to check it right away. I waited 25 mins and when he checked it, I revved it up and he didn't see anything. When I got home I didn't see anything. That was a first long drive in a while. I didn't use the highways. I got up to 35 mph only. I still have to test run everything. I have to get up to 50 mph. To make sure no bolts or anything come out.

And yes he did mention some kind of silicone or some kind of paste to keep the new one sticking on there. Not a lot, just to keep it on there to prevent it from moving. He said if I was going to do it myself. I'm still happy with this mechanic (He is very fair and honest) (He looked at my car for free and offered advice). So, I'm not complaining. Things are going well. And I didn't have to spend too much money. I'm very happy this car has been maintained very well throughout its years.

Another thing is the ring is still kind of new. When I had him put it in this year. So maybe it's resealing with the new heat again. Maybe I can get lucky and test it out again, and make sure there is no exhaust leak.

 

For those rings, I slather them in Ultra Copper Permatex. It seems to help them seal better. My Toyota want to be uses 4 of them on the exhaust system.